1. Technical Field
The present invention relates to the field of electronic assembly and more specifically to the manufacture and assembly of flexible circuits by molding and plating of electrical and electronic interconnections without the use of solder.
2. Background Art
The assembly of flexible circuits, and more specifically the permanent assembly of package IC components and discrete electronic components (e.g., chip resistors, chip capacitors, diodes, etc.) to the outer surfaces of flexible circuit boards, has involved the use of some form of relatively low temperature solder alloy (e.g., Sn63Fb37) since the earliest days of the electronics industry. The reasons for using solder assembly are numerous, but can be summarized by noting here that it has long served well to allow for the mass joining of thousand of electronics interconnections between printed circuits (rigid or flexible) and the leads of electronic components.
While solder alloys have been most common, other joining materials have been proposed and/or used, including isotropic and anisotropic adhesives or so-called “polymer solders” which are a form of conductive adhesive. In some cases even non-conductive adhesives have also been suggested. Moreover, there have been efforts to make connections separable by providing sockets for components, to facilitate removal and replacement if needed or desired. In addition, there have also been electrical and electronic connectors developed to link power and signal carrying conductors with various resilient contact structures, but all of which require constant applied force or pressure.
Adhesive and socket solutions are attractive for some applications because they do not require exposing components mounted on them to high temperatures, however, each of these solutions also has limitations related to cost, performance, reliability, and combinations thereof. Current generation adhesives are not as conductive as electronic solder and sockets, while they allow for easy component removal and replacement. They also add unwanted weight and are expensive.
In recent years the electronics industry has been forced by European Union legislation to eliminate the element lead (Pb) from solder, based on a presumption of risk to humans which has yet to be proven. However, the impact of this legislation has been deleterious to the electronics industry as electronic assemblies are less reliable because of the higher temperatures required. In addition, the energy used to obtain the higher temperatures has been damaging to the environment. Present day technical and trade journals for the electronics industry are replete with articles and technical papers describing problems associated with lead-free soldering and research into ways to make the problem less onerous. The high temperatures of soldering significantly reduce the number of options available for use as a prospective substrate and tend to force the user to employ higher temperature materials.
Given the aforementioned problems in the assembly of flexible circuits with solder, especially for lead-free solders, there is room for further improvement in flexible circuit assembly technology.